The invention relates to an arrangement for measuring the thickness of thin layers which can be applied on workpieces or substrates during the coating of the latter while being conveyed through the process chamber. The thickness measuring is carried out by detecting transmission, reflection or resistance properties or by mechanically measuring the thin layer.
A test glass support for the optic measurement of layer properties is known (German patent No. 29 32 483) having several indentations for test glasses which are equidistantly arranged in a circle on a plate. A drive shaft serves to move the glasses, one at a time, in a transfer movement into the flow of coating material and into the beam of a measuring light; each of the test glasses is associated with a certain coating material so as to always provide the same coating material to be intermittently deposited on the same test glass. This test glass support is used for vacuum coating systems having a carousel which can rotate around a central axis and includes at least one substrate holder which in turn can be exposed to different coating materials in different positions. In order to accomplish the object of rotating or transferring the test glasses during a period of rotation or transferring of the substrate holder into a new coating position, the invention suggests providing the drive shaft of the plate for the test glasses with a first driving wheel which is coupled with a second driving wheel which in turn is concentric with respect to the center axis; the transmission ratio is selected such that whenever the substrate holder is moved into a different position, a different test glass is transferred into the flow of coating material and into the measuring light beam. The test glass support is necessarily coupled with the carousel of the substrate holder such that a wrong correlation is avoided.